Studies on the adsorption of heptamolybdate ions on AISI 304 stainless steel from acidic HCl solution for corrosion inhibition

Abstract

Surface interaction of heptamolybdate ions Mo7O24 6- on ASI 304 stainless steel (SS) greatly reduces the corrosion rate of the material in acid environments, providing an environmentally-friendly inhibitor system. Corrosion inhibition properties have been studied in naturally aerated 0.5 M HCl solution from weight loss measurements. The influences of inhibitor concentration and solution temperature were investigated. The percentage inhibition efficiency, SW(%), increased for increasing concentrations of the ionic inhibitor species. Conversely, the increase of temperature decreased the inhibition efficiency. That is, the corrosion rate, vcor, was faster at higher temperature whereas it was slower for increasing inhibitor concentrations. The adsorption of the inhibitor ions onto the SS surface was found to follow the Langmuir adsorption isotherm. The values of the standard adsorption free energy, 0 ads G , are consistent with a spontaneous physisorption mechanism of the inhibitor ions on the surface of the steel.